NAT in Routed Mode

The following figure shows a typical NAT example in routed mode, with a private network on the inside.

NAT Example: Routed Mode

  1. When the inside host at 10.1.2.27 sends a packet to a web server, the real source address of the packet, 10.1.2.27, is translated to a mapped address, 209.165.201.10.

  2. When the server responds, it sends the response to the mapped address, 209.165.201.10, and the threat defense device receives the packet because the threat defense device performs proxy ARP to claim the packet.

  3. The threat defense device then changes the translation of the mapped address, 209.165.201.10, back to the real address, 10.1.2.27, before sending it to the host.